1. Field of the Invention
The present invention relates to a carriage controlling apparatus for a storage device such as, for example, for use in a floppy disk drive system. The invention includes both apparatus and method of the discriminating.
2. Description of the Related Art
In a general floppy disk drive system, a floppy disk drive (FDD) is provided with a mechanism for moving a carriage with a magnetic head in a radial direction of a recording medium, such as a floppy disk. As such a mechanism, a lead screw mechanism is known, which uses a lead screw rotatively driven by a stepping motor. The lead screw has a spiral groove. A needle coupled with the carriage engages the groove. When the lead screw is rotated by the motor, the needle converts a rotating motion into a rectilinear motion, and transfers it to the carriage. The carriage is generally provided with a pair of heads, an S0 head for the side 0 of the recording medium and an S1 head for the side 1. When the lead screw is rotatively driven, the carriage with the paired heads rectilinearly moves in the radial direction for seeking a destination track on the recording medium. The paired heads, when positioned at the destination track, applies a read/write operation to that track.
The FDD of the 5.25-inch type, for example, comes in two varieties, the 48TPI mode FDD for a recording medium whose track density is 48TPI (track per inch) and the 96TPI mode FDD for a recording density of 96TPI. The 96TPI mode FDD is able to read data out of the recording medium of 48TPI, but the 48TPI mode FDD is unable to write data on and read data from the recording medium of formatted in the 96TPI mode. Therefore, the host computer in the floppy disk drive system must discriminate the format mode of an FDD used, i.e., between the 48TPI mode or the 96TPI mode. A known system to discriminate the mode of the FDD exists. In this system, an FDD is connected to a floppy disk drive system. A floppy disk as a recording medium is set to the FDD. The carriage is moved from the outer side of the floppy disk to the inner side, and vice versa, i.e., a reciprocal seek operation is performed. According to the number of tracks (seek distance) over which the carriage has been reciprocated, the host computer determines the TPI mode of the FDD used in the floppy disk drive system.
To be more specific, the paired heads (referred frequently to as a head) are moved from the outermost track on the floppy disk (track 0) as a reference track to the innermost track (45 track of the floppy disk of 48TPI, for example). This stroke of the head or carriage is called a forward seek operation. Then, the head is moved reversely, viz., from the innermost track to the outermost track. This stroke is called a reverse seek operation.
The host computer compares the number of step pulses (FS) obtained through the forward seek operation with that (RS) obtained through the reverse seek operation. The step pulses are contained in a STEP signal for driving a stepping motor as a drive source for the carriage. The STEP signal is produced by a floppy disk controller (FDC), and is then applied to a control circuit (containing a microprocessor as a major component) for the FDD. Ordinarily, the head is moved one track every step pulse. A seek distance caused by one step pulse in the 48TPI mode FDD is the double of that in the 96TPI mode FDD. Accordingly, a seek distance corresponding to 45 tracks in the 48TPI mode FDD is equal to that corresponding to 90 tracks in the 96TPI mode FDD.
When the number of step pulses FS is equal to that RS, FS=RS, the host computer decides that the FDD used is a 96TPI mode FDD. When FS&gt;RS, it decides that the FDD is of the 48TPI mode. When a STEP signal consisting of 45 pulses, for example, is produced, in the case of the 48TPI mode FDD, the carriage hits against a carriage stopper at the position corresponding to 42 tracks, to a standstill, in the forward seek mode. In the reverse seek mode, the carriage moves from the position of 42 tracks where it was stopped in the forward seek mode, to the track 0 of the reference track. A track-zero sensor installed in the FDD detects that the carriage reaches the track 0, and generates a signal. The FDC receives this signal from the FDD and stops the outputting of the STEP signal. It is understood that in the reverse seek mode, 42 pulses of the STEP signal are produced. The number of step pulses (45 pulses) in the forward seek mode is larger than that (42 pulses) in the reverse seek mode.
In the FDD discriminating system as mentioned above, in the case of the 48TPI mode FDD, when the carriage collides against the carriage stopper in the forward seek mode, there is the possibility that the needle of the lead screw mechanism will slip off the groove. If the needle slips off, it runs on the surface of the lead screw to a standstill. Under this condition, if the forward seek mode is switched to the reverse seek mode, the lead screw reversely rotates and the needle slips in the grooves again. A STEP signal in the reverse seek mode is outputted from the FDC during the transient period that the needle on the lead screw slips into the groove. Accordingly, 45 pulses sometimes have been produced till the carriage moves and reaches the track 0. If so, FS is equal to RS although the FDD now used is of the 48TPI mode. On this fact, the host computer mistakenly recognizes that the FDD used is a 96TPI mode FDD.
Thus, in the FDD mode discriminating system which discriminates the FDD mode on the basis of the data obtained by the reciprocal seek operation, the needle of the lead screw mechanism slips off the groove of the lead screw. The seek distance of the head sometimes fails to amount to the number of step pulses. The host computer mistakenly recognizes the TPI mode of the FDD used, leading to incorrect TPI mode discrimination.